Tech investors brace for a cruel summer

FORTUNE – Summertime may be when the living is easy for many people, but not for tech investors this year. As the time draws near for many companies to report their second-quarter earnings, a last-minute sense of unease is setting in among investors and analysts.

Since investors returned from their 4th of July holidays, the Nasdaq Composite has lost 4%, while many of the bigger names in tech have lost even more. Microsoft MSFT is down 6%, while IBM IBM and Cisco CSCO are off 7% and Intel INTC has fallen 8%. In most cases, the declines have been accompanied by analysts warning of a weaker second-quarter than they had previously expected.

And things aren’t looking much better for the rest of the year. Thursday morning, IT-outsourcing giant Infosys INFY fell 12% after the company warned that business would slow down in the second half of 2012, citing the loss of big contracts among banks and other companies. “The environment today for us is more challenging than what it was in April,” said Infosys CEO S. D. Shitulal.

There isn’t one overriding reason for the recent round of tech jitters, but several. The financial turmoil that plagued Europe in the quarter, along with the cooling of China’s economy; the rise of disruptive technologies that are hurting big tech companies that have been slow to adapt; and the tendency of analysts to be optimistic in times of uncertainty.

The largest tech companies have long been dependent on global markets, but in the second quarter, every major market faced challenges. Economic growth showed signs of stalling in the U.S., while China’s economy cooled. But the biggest concern was in the European Union, where unemployment rose to 11% and some countries slipped back into recession.

EU leaders have dragged their feet in solving the debt crisis, prolonging a sense of uncertainty among companies and prompting consumers to hold back on buying new gadgets. A survey by Computer Economics found that 31% of companies surveyed are planning to cut operational IT spending in the coming year, against 16% that plan to spend more. To shore up profits, companies are cutting costs, and that includes money for new technology.

A separate report from Gartner said that global IT spending would rise incrementally to $3.6 trillion in 2012 from $3.5 trillion last year. Gartner noted that spending on some areas of tech will see more growth than others: Cloud computing, for example will receive $109 billion in IT spending this year, up from $91 billion in 2011.

While that’s good news for cloud companies, it’s not necessarily good for other tech giants. Companies are spending on cloud technologies because it can be more efficient and cheaper than installing and maintaining older software systems. But money spent on lower-cost cloud systems means money not spent on proprietary software, which is often more expensive. Companies like Oracle ORCL and IBM are investing in cloud computing, even if it risks cannibalizing their older programs.

A similar kind of disruption is happening in the PC industry, an area where companies and consumers spend heavily. When people are buying PCs they are buying tablets or low-cost PCs from Asian companies. Overall, PC shipments fell 0.1% in the second quarter from the same quarter in 2011, to 87.5 million, according to Gartner. For U.S. makers, the fall was much worse: HP HPQ and Dell DELL both shipped 12% fewer PCs in the second quarter.

These are not the kind of numbers to encourage investors into believing tech stocks will post strong earnings. Already some of them have been signaling that investors shouldn’t get too excited. In the past week, Advanced Micro Devices AMD, Applied Materials AMAT and Informatica INFA warned of disappointing earnings. According to Factset, 24 companies in the S&P 500 issued negative guidance for the second quarter, 50% more than the five-year average.

And if that’s not worrying, consider this. Factset estimates that tech stocks in the S&P 500 will post earnings growth of 3.6% for the quarter. While that’s higher than the 3% rate for all of the S&P 500, it’s all Apple AAPL. Exclude Apple’s expected earnings growth and average tech earnings will fall 2%.

There’s even concern over Apple’s earnings. The cannibalization of laptops by tablets may be eating into sales of big-ticket Macbooks, an analyst at BMO Capital said. Other analysts are concerned that, with the release of a LTE-friendly iPhone all but assured this fall, many Apple loyalists are waiting to buy iPhones, slowing sales for the next several months.

Another potential factor is that analysts in general tend to lean toward optimism in earnings forecasts. They often rely on the guidance from companies, and corporate managers are loathe to telegraph bad news – like the Infosys warning – until they are absolutely sure of a slowdown. If more warnings of a slowdown follow, expect a round of hearty downward revisions of tech earnings in general.

For investors, there are a couple of silver linings in the event of a tech slowdown. Longer-term, tech remains a strong sector: Companies can only cut back on IT for so long without hurting their own competitive edge. And there remain some key areas of strength. Companies active in mobile and cloud computing, for example, are doing much better than PC makers and chip manufacturers.

For tech investors in general, however, the next few weeks of earnings reports could be a volatile ride.